User-defined functions in C consist of several elements:

• Function Declaration:
  The function declaration provides the compiler with information about the function's name, return type, and parameters (if any).
  Example:
  int addNumbers(int a, int b);
• Function Definition:
  The function definition contains the actual implementation of the function, specifying what it does.
  Example:
  int addNumbers(int a, int b) {
  return a + b;
  }
• Return Type:
  The return type specifies the type of data that the function will return.
  Example:
  int in int addNumbers(int a, int b);
• Function Name:
  The function name is an identifier used to call the function.
  Example:
  addNumbers in int addNumbers(int a, int b);
• Parameters:
  Parameters are variables that the function accepts as input. They are declared within the parentheses.
  Example:
  (int a, int b) in int addNumbers(int a, int b);
• Function Body:
  The function body contains the statements that define the logic of the function.
  Example:
  int addNumbers(int a, int b) {
  return a + b;
  }
• Return Statement:
  The return statement specifies the value that the function sends back to the calling code.
  Example:
  return a + b; in the addNumbers function.

Here's an example combining these elements:

Program.c
#include <stdio.h> // Function declaration int addNumbers(int a, int b); int main() { // Function call int result = addNumbers(5, 7); // Output the result printf("Sum: %d\n", result); return 0; } // Function definition int addNumbers(int a, int b) { return a + b; }

Output:
Sum: 12